Luminescence techniques in radiation dosimetry have traditionally been dominated by thermal methods in which a sample (a thermoluminescence dosimeter, or TLD) is exposed to radiation and is then heated in the dark. At a certain temperature, or in a certain temperature range (either of which is dependent upon the material used and the detailed parameters of the heating procedure), luminescence is emitted from the material. The intensity (for example, the integrated light emission between two specified temperatures) is related, by calibration procedures, to the original absorbed dose of radiation. This method of radiation dosimetry has been described in the literature, and has been in general usage, for approximately four decades.
However, in many circumstances optically stimulated luminescence (OSL) has proven to be a superior method of measuring radiation dose. Generally speaking, OSL methods illuminate a previously irradiated dosimeter with light of a particular frequency and intensity. This exposure excites light production within the dosimeter by transfer of charges from traps to luminescence centers. Then, by measuring the intensity and duration of the resulting luminescence signal that is emitted from the dosimeter, an accurate measure may be obtained of the amount of radiation to which the dosimeter was exposed.
As useful as OSL has proven to be, its conventional application has certain shortcomings. More particularly, there is a general departure from linearity in the luminescence/dose curve at higher dose levels and it is susceptible to saturation effects. Further, conventional OSL is not suitable for use in real-time measurement of radiation dose such as would be useful in the treatment of medical disorders by radiation. Instead, conventional OSL dosimetry attempts to determine absorbed doses only after the radiation exposure has ceased using post-irradiation analysis of the OSL signal.
Methods and dosimeters employing optically stimulated luminescence in the detection of radiation exposures in various configurations are described in U.S. Pat. Nos. 5,030,834; 5,091,653; 5,567,948; 5,569,927; 5,732,590; 5,811,822; 5,892,234; 5,962,857; 6,087,666, 6,316,782; and 6,414,324, which patents are fully incorporated herein by reference as if set out at this point.
Heretofore, as is well known in the radiation dosimetry industry, there has been a need for an invention to address and solve the above-described problems. Specifically it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a system and method that would address the issue of determining the absorbed radiation dose in real time during the radiation exposure using OSL.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.